Material Model Development for Impact Analysis of Oriented Polypropylene Foam Structures 2001-01-0310

Federal legislation for head impact protection in upper automotive interiors (FMVSS 201U) has presented a unique energy management problem for the automotive industry. Due to extremely tight packaging conditions, energy absorbers are required to have efficiencies which exceed those of traditional foam materials, and force the development of new methods of energy absorption.

The push toward shortened design cycle times has required the use of predictive engineering tools such as finite element analysis. Predictive tools which can accurately drive design direction reduce design cycle times, costs associated with multiple prototype part builds, and costs associated with physical testing. Over the last few years, the inclusion of FMVSS 201U energy absorbing countermeasures in the upper interior trim has been largely experimental in nature, yielding solutions which are costly in both time and money. This paper presents a characterization for a class of oriented polypropylene foams which have orthotropic properties, and exhibit energy absorption efficiencies in the range of 80%–90%. Material characterization data was processed for input into the LS-DYNA^® explicit finite element code. Completed material models were used to generate predicted response characteristics of oriented foam structures under FMH (free motion headform) testing, allowing comparison between predicted and experimentally measured responses.